The proposed experimental and theoretical developments aim to elucidate the nature and scope of hemispheric specialization, independence, interaction and control in the human brain. Coordinated experiments will be carried out with normal subjects and neurological patients using convergent behavioral, anatomical and physiological methods and addressing general issues in cognitive neuroscience, notably concerning modularity and intermodular communication. Technological developments include a computerized system for human neuropsychological testing including an eyetracker-based hemianopsia simulator for analyzing hemispheric differences in processing complex visual arrays. A core set of behavioral experiments (1) explores individual differences in hemispheric specialization in attention, perception and language, (2) contrasts different degrees of hemispheric independence, including independence of strategies, resources and priming, and (3) analyzes the control of parallel processing in the two hemispheres. In the second part of the proposal, the same experiments will be administered to (1) patients with chronic complete cerebral commissurotomy, (2) patients with agenesis of the corpus callosum, and (3) patients with partial callosotomy, both pre- and post-surgically. In the third part of the proposal we will study the anatomical correlates of the same behavioral measures of interhemispheric relations. We will (1) analyze the cytoarchitecture of asymmetric cortex and its relation to regional callosal morphology and morphometry in post mortem, and (2) analyze morphometric-behavioral correlations between "volumes-of- interest" and regional callosal morphometry from in-vivo MRI in normal subjects who also received the behavioral measures. In the fourth part we will study the physiological correlates of the same behavioral measures by monitoring trial-based topographic EEG as an index of hemispheric activation (alpha suppression) and interhemispheric interaction (coherence). The physiological measures will be applied to the normal subjects as well as to the patient populations. Results promise better understanding and possible control of pathology due to abnormal cerebral activation or impaired interhemispheric communication. The data will contribute to theoretical cognitive neuroscience by clarifying how independent, parallel cortical processing modules of attention, perception, and language interact.